Assessing populations of eastern brook trout (Salvelinus fontinalis) above and below waterfalls in mountain streams of Virginia

Anthropogenically driven factors, such as increasing temperature and sediment in valley streams, acidification of mountain streams, and the introduction of non-native trout, are restricting habitat suitable for healthy populations of eastern brook trout (Salvelinus fontinalis) throughout their native Appalachian range. Brook trout are important as predators of insects in mountain streams and as a favorite of anglers. It is crucial that remaining populations in sustainable habitats be identified and preserved. Waterfalls are geologic knickpoints preventing base-level lowering that create unique, stable landscapes above them, which may alleviate the temperature-productivity/acidity “habitat squeeze” for populations of brook trout and could serve as potentially ideal targets for conservation efforts despite being isolated. This study investigates brook trout occurrence above waterfalls in Virginia and compares brook trout populations found above waterfalls to those below them. One-hundred meter reaches above and below seven waterfalls in Virginia’s George Washington and Jefferson National Forest were sampled for brook trout via 3-pass, block-netted, backpack electrofishing depletions. All brook trout were counted, weighed, and measured for fork length. The response variables are differences in 1) percent dominance, 2) population size, 3) biomass, and 4) length-weight index (Fulton’s Condition Factor) between brook trout above and below waterfalls. Brook trout dominance (100 vs. 36.9%) is greater above than below waterfalls, but not significantly (p = 0.1003). We found abundance (26 vs.12 individuals per 100m) and overall biomass (885.3 vs 284.6 grams per 100m) of brook trout populations above waterfalls to be significantly greater than their below waterfall counterparts (p = 0.078 for both). We also found brook trout above waterfalls to have a higher condition factor (1.086g/cm3 vs 1.0636g/cm3) than those below waterfalls (p = 0.031). Lastly, we found populations above waterfalls where their occurrence was previously unknown. Despite being isolated, brook trout populations above waterfalls were just as if not more robust than those below and may be excellent targets for conservation.